Salivary glands are often incidentally irradiated either in low dose ranges, for diagnostic purposes, or at higher dose ranges for therapeutic purposes. Often, little attention is paid to these glands clinically since, by some definitions of radiosensitivity, they would be regarded as radioresistant. It is well-known, however, that a syndrome of dry mouth with acute swelling, tenderness, and pain of the parotid follows irradiation. Several studies based on light microscopy described x-irradiation damage of salivary glands, but our recent paper was the first to describe changes by electron microscopy wherein damage was detected as early as 3 hours. The present study seeks to analyze the effects of irradiation upon parotid secretion and synthesis. Specifically investigated will be a) the action of x-rays as an inducer of immediate secretion (secretogue), b) the capacity of the injured gland to release, upon stimulation, secretory product at varying times after irradiation, c) the ability of the injured gland to re-synthesize secretory product and d) the ultrastructural pathway and time course of secretion in the x-ray injured gland. These aspects of the parotid's function will be carried out by electron microscopy, by electron microscopy autoradiography and by biochemical assay of amylase.